Wireless communication systems are well known in the art. A typical wireless communication system in accordance with current 3GPP specifications is depicted in FIG. 1. By way of example, the network architecture shown in FIG. 1 is that of UMTS. The UMTS network architecture includes a Core Network (CN) interconnected with a UMTS Terrestrial Radio Access Network (UTRAN) via an interface known as Iu which is defined in detail in the current publicly available 3GPP specification documents. The UTRAN is configured to provide wireless telecommunication services to users through wireless transmit/receive units (WTRUs), known as User Equipments (UEs) in 3GPP, via a radio interface known as Uu. The UTRAN has one or more Radio Network Controllers (RNCs) and base stations, known as Node Bs in 3GPP, which collectively provide for the geographic coverage for wireless communications with WTRUs. One or more Node Bs are connected to each RNC via an interface known as Iub in 3GPP. The UTRAN may have several groups of Node Bs connected to different RNCs, two are shown in the example depicted in FIG. 1. Where more than one RNC is provided in a UTRAN, inter-RNC communication is performed via an Iur interface. Communications external to the network components are performed by the Node Bs on a user level via the Uu interface and the CN on a network level via various CN connections to external systems.
In general, the primary function of Node Bs is to provide a radio connection between the Node Bs' network and the WTRUs. Typically a Node B emits common channel signals allowing non-connected WTRUs to become synchronized with the Node B's timing. In 3GPP, a Node B performs the physical radio connection with the WTRUs. The Node B receives signals over the Iub interface from the RNC that control the radio signals transmitted by the Node B over the Uu interface.
A CN is responsible for routing information to its correct destination. For example, the CN may route voice traffic from a WTRU that is received by the UMTS via one of the Node Bs to a public switched telephone network (PSTN) or packet data destined for the Internet. In 3GPP, the CN has six major components: 1) a serving General Packet Radio Service (GPRS) support node; 2) a gateway GPRS support node; 3) a border gateway; 4) a visitor location register; 5) a mobile services switching center; and 6) a gateway mobile services switching center. The serving GPRS support node provides access to packet switched domains, such as the Internet. The gateway GPRS support node is a gateway node for connections to other networks. All data traffic going to other operator's networks or the internet goes through the gateway GPRS support node. The border gateway acts as a firewall to prevent attacks by intruders outside the network on subscribers within the network realm. The visitor location register is a current serving networks ‘copy’ of subscriber data needed to provide services. This information initially comes from a database which administers mobile subscribers. The mobile services switching center is in charge of ‘circuit switched’ connections from UMTS terminals to the network. The gateway mobile services switching center implements routing functions required based on current location of subscribers. The gateway mobile services also receives and administers connection requests from subscribers from external networks.
The RNCs generally control internal functions of the UTRAN. The RNCs also provide intermediary services for communications having a local component via a Uu interface connection with a Node B and an external service component via a connection between the CN and an external system, for example overseas calls made from a WTRU in a domestic UMTS.
Typically, an RNC oversees multiple Node Bs, manages radio resources within the geographic area of wireless radio service coverage serviced by the Node Bs, and controls the physical radio resources for the Uu interface. In 3GPP, the Iu interface of an RNC provides two connections to the CN: one to a packet switched domain and the other to a circuit switched domain. Other important functions of the RNCs include confidentiality and integrity protection.
An RNC has several logical roles depending on the CN's needs. Generally, these functions are divided into two components: a serving RNC (S-RNC) and a controlling RNC (C-RNC). As a serving RNC (S-RNC), the RNC functions as a bridge to the CN and the Node Bs. As a controlling RNC (C-RNC), the RNC is responsible for the configuration of a Node B's hardware. The C-RNC also controls data transfers and handles congestion between different Node Bs. A third logical role of an RNC is as a Drift-RNC. As a Drift-RNC, the RNC is responsible for handing off the WTRU to another Node B as the WTRU traverses the coverage area.
The RNCs and the Node Bs together perform radio resource management (RRM) operations, such as “inner loop power control.” This is a feature to prevent near-far problems. Generally, for example, if several WRTUs transmit at the same power level, the WRTUs closest to a Node B may drown the signals from the WRTUs that are farther away. The Node B checks the power received from the different WRTUs and transmits commands to the WRTUs to reduce or increase power until the Node B receives the power from each WRTU at about the same level.
Conventionally, a Node B will provide wireless communication for many WTRUs. Node Bs will typically handle multiple communications with subscriber systems concurrently. One measure of Node B capacity is the maximum number of concurrent communications it can support which is a factor determined by such things as available power and bandwidth.
Since not all subscribers communicate with the Node B at the same time, a Node B can provide wireless service to a great many subscribers beyond its capacity for concurrent communications. If the maximum number of concurrent communications for a Node B is being conducted, an attempt to establish a further communication will result in an indication of service unavailability, such as a system busy signal.
Service coverage by a Node B is not only limited to its capacity for handling concurrent communications, but is also inherently limited to a specific geographic area. A Node B's geographic range is typically defined by the location of the Node B's antenna system and the power of the signal broadcast by the Node B.
In order to provide wireless service over an expansive geographic area, a network system is conventionally provided with multiple Node Bs. Each Node B has its antenna system selectively physically located to provide coverage over a specific portion of the total geographic area which is covered by the system. Such systems readily provide wireless service for WTRUs which can travel out of the range of one Node B and into the range of another Node B without interruption of an ongoing wireless communication. In such networks, the geographic area covered by a Node B is commonly referred to as a cell and the telephone communication services provided are commonly called cellular telephone services.
In designing a wireless communication system to cover a specific geographic area, the geographic area may be partitioned into a predefined pattern of cells. For example as illustrated in FIG. 2A, hexagonal-shape cells can be defined so that the cells cover the entire geographic area in a honeycomb pattern. In such a system, each cell can have a Node B which has an antenna at the center of the cell to provide 360° coverage. Although a map of cell coverage may be designed without any overlapping areas, in practice as shown in FIG. 2B, the transmission beams, shown in phantom, from Node B antennas of adjacent cells do overlap. This overlap of beam coverage enables “handover” of a communication being conducted by a WTRU from one Node B to another as the WTRU travels from one cell to another. However, an overlapping Node B signal contributes to interference of a signal received by a WTRU from a different Node B when the WTRU is located in the overlap area.
To more readily meet service demands and reduce interference, beam-forming may be used. Beam-forming in communications is a very useful tool, and is implemented by using an array of antennas for transmission, reception or both, in such a manner that will best match the channel requirements. The phase and amplitude of the signals in each antenna are precisely controlled so as to obtain a constructive pattern at the receiver.
Known methods of beam-forming have addressed adjustment of the beams in the horizontal direction. Additionally, in prior art, transmission-power adjustment or deployment of wide vertical beams for receiving signals have been used to match the channel requirements. This technique helps to cope with severe multipath situations and overcomes extra attenuation by providing extra effective power concentration. Beam-forming has also been utilized in handling interference from other transmission sources.
Although beam forming provides many benefits, present implementations cause various issues that need to be addressed. By way of example, present implementations of beam-forming suffer from the beams intruding on adjoining cells. The intrusion can be to/from a neighboring cell and is sometimes especially pronounced if the beam-forming includes a broad vertical beam component to reach WTRUs. Furthermore, objects, terrain, etc. also interfere with the vertical component of wide beams.
It is therefore desirable to obviate the disadvantages encountered in known implementations of beam-forming.